A colony of approximately 5,500 athymic mice has been established. Thirty different human tumors are now being carried in the athymic mice. Studies on the factors which regulate growth of the human tumors in the athymic mice are being pursued. Some of the human tumors, after growth in the athymic mouse, have been established in culture. Chemotherapeutic studies have been initiated on using the athymic mouse human tumor system as a model for chemotherapeutic treatment in patients. Conditions which will promote optimum growth of the human tumors grown in tissue culture are also being investigated. The effect of the human tumors on the athymic mouse immune system is also being studied with respect to the induction of mouse lymphomas.